Page:The Osteology of the Reptiles.pdf/39

Rh with the prevomers is lost in some Cynodontia (Fig. 43 ) and Rhiptoglossa. Teeth are generally present in the Theromorpha, Rhynchocephalia, and Squamata, and in some Therapsida and "Pseudosuchia." In the early reptiles (Figs. 6, 21, 24, 40 ) they are more or less loosely articulated with the basipterygoid process of the basisphenoid, as in most modern reptiles, but are fixed in the Therapsida (Fig. 43 ) and not a few others. There is an interpterygoidal space between them partly filled with the parasphenoid rostrum in the early reptiles (Figs. 6, 21 ), as in the Plesiosauria (Fig. 47 ), Rhynchocephalia, most Squamata (Fig. 55 ), etc.

In some Therapsida (Fig. 43 ), Nothosauria (Fig. 47 ), Placodontia (Fig. 49 ), they unite along the whole middle line. There is a theory that the pterygoids are the real homologues of the mammalian alisphenoids.

Ectopterygoids (ec). The ectopterygoids (transpalatines) have not yet been certainly demonstrated in the early Cotylosauria, though perhaps present; they are certainly absent in some of the Temnospondyli. They have been recognized in all other orders except the Ichthyosauria and Chelonia, connecting the pterygoids with the posterior end of the maxillae, back of the palatines; sometimes also with the jugals in the Squamata (Fig. 55 ). Most remarkable are their relations in Pteranodon (Fig. 72 ) of the Pterosauria, where they pass above the palatines to unite with the pterygoid. The ectopterygoids are believed by some to be the homologues of the pterygoid process of the alisphenoid of the mammals.

Epipterygoids (ep). A pair of bones articulating below with the pterygoids, above with the parietals (Fig. 8). They have been observed in the Temnospondyli, various genera of the Cotylosauria, Theromorpha, and Therapsida, and are probably generally present in reptiles, though absent in the Crocodilia, many Chelonia, the